1. Field of the Invention
The present invention relates to means for assembly longitudinal body, such as a Surface Acoustic Wave (SAW) component within a housing or capsule (package).
2. Background Information
SAW components or devices are characterized by the use of a piezoelectric crystal substrate with electro acoustic transducers, normally a metal film forming an interdigital `finger` pattern, deposited onto the crystal surface. The transducer produces an electric field over the crystal surface when an electric signal is applied to it. This electric field is transformed into a mechanical force in the crystal, which subsequently launches an acoustic (mechanical) wave in the crystal surface.
Conversely, the transducer may convert the acoustic energy back to an electric signal. The most commonly used substrate materials are quartz, lithium niobate and lithium tantalate. These materials are, by their nature, sensitive to mechanical stress. Any mechanical stress will influence the electrical behavior of the SAW component.
SAW components usually have a longitudinal structure, i.e., the length is greater than the width, and they are usually glued along one of its surfaces to the bottom of a housing or capsule. This assembling method can be considered suitable for smaller SAW components, such as those having a length of less than 20-30 mm, and for SAW devices with moderate electric performance requirements over the operating temperature range. When larger SAW components are concerned, and when both the electrical performance requirements and the operating temperature range are demanding, other assembling means are required, in order to avoid degradation of the electrical performance of the SAW component due to mechanical stress introduced by the differential coefficient of thermal expansion between the SAW substrate and the capsule.
An alternative, well known approach is to isolate the entire SAW component and its capsule thermally, e.g., by use of a temperature controlled heater. This method is however in many cases impracticle or unacceptable for cost or other reasons.